The previous work has demonstrated that human endothelial cells (EC) can activate allogeneic T lymphocytes to secrete IL-2 and to proliferate.The EC signals involved in triggering T cell activation include expression both of cytokine-inducible class I and class II major histocompatibility complex (MHC) molecules (for activation of CD8+ and CD4+ T cells, respectively) and of membrane "costimulator" molecules, including LFA-3 (CD58) and as yet unidentified proteins. In this application, they propose to use monoclonal antibody blocking strategies to identify additional molecules involved in CD4+ and CD8+ T cell activation by allogenic EC and then to optimize conditions for reducing the expression of such molecules, using antisense oligonucleotides, retrovirus encoded antisense RNA, primary amines or "decoy" promoter oligonucleotides. They will test such modified EC in four established in vitro assays of lymphocyte activation to determine if the ability to activate T cells is correspondingly reduced.Specifically, they will assay: T cell proliferation induced by allogenic EC; T cell IL-2 production induced by allogeneic EC; limiting dilution analysis of T cell IL-2 production induced by allogenic EC; and EC-mediated costimulation of T cell IL-2 production induced by phytohemagglutinin. They will examine EC in human skin or in synthetic vascular networks that have been transplanted into SCID mice previously or subsequently reconstituted with a human immune system, to test for the ability of EC to activate T cells in vivo. Finally, this model will be used to determine whether modified EC have reduced ability to cause T cell activation and immune-mediated injury in vivo, assessed by high resolution morphologic techniques. These experiments could serve as a new approach to reducing immune-mediated injury, and may open new approaches for EC transplantation.